Absorption spectroscopy techniques

Differential absorption spectroscopy techniques were used to determine absolute species concentrations (C2H4, CO, and CO2) by tuning the wavelength of the lasers across transitions near 1646 nm (i/i +1 9, t 5 + < 9 bands of C2H4), the i 13 transition of CO (3z/ band) near 1564 nm, and the R16 transition of CO2 near 1572 nm 2ui + 2v2 + V9 band). The absorption measurements were recorded in the multipass cell. 

In principle, absorption spectroscopy techniques can be used to characterize radicals. The key issues are the sensitivity of the method, the concentrations of radicals that are produced, and the molar absorptivities of the radicals. High-energy electron beams in pulse radiolysis and ultraviolet-visible (UV-vis) light from lasers can produce relatively high radical concentrations in the 1-10 x 10 M range, and UV-vis spectroscopy is possible with sensitive photomultipliers. A compilation of absorption spectra for radicals contains many examples. Infrared (IR) spectroscopy can be used for select cases, such as carbonyl-containing radicals, but it is less useful than UV-vis spectroscopy. Time-resolved absorption spectroscopy is used for direct kinetic smdies. Dynamic ESR spectroscopy also can be employed for kinetic studies, and this was the most important kinetic method available for reactions... 

Interest in X-ray absorption spectroscopy techniques and particularly in EXAFS, XANES and SEXAFS, has increased enormously since synchrotron radiation facilities were developed at Stanford University 1974. X-ray absorption spectroscopy is a powerful tool in determining the local structure near a particular atom. X-ray absorption spectra of a surface atom can be divided in two parts ... 

In this paper, a fiber optic remote sensing multiplexed oxygen monitoring system is designed based on tunable diode laser absorption spectroscopy technique. It is an intrinsic sensing method to provide long term stability without the need of frequent calibrations. 

The aim of this study is to compare several physico-chemical measurements, employing electrochemical and electronic absorption spectroscopy techniques, and thereby obtain a better understanding and knowledge of the chemistry of the LiCl-KCl-KaMoCle solutions. 

The reactions between tyrosine and radiolyticaily generated OH radicals have been investigated by Solar et al [42], in neutral N20-saturated aqueous solution. They employed a combination of pulse radiolysis and time-resolved absorption spectroscopy techniques, and were able to determine the relative yields and reaction rates for addition to different ring sites as well as for subsequent water elimination from the ortho position and for direct abstraction of the phenolic hydrogen. Figure 2 summarizes their results. As seen, the predominant addition site is at the ortho position, and the reaction rates for OH addition or direct H-atom abstraction are 10 -10 times faster than the water elimination fi om the ortfm adduct. 

Frequency-modulation spectroscopy can also be used for sensitive absorption measurements using pulsed lasers [9.184]. The sidebands are then generated by microwaves ( 10GHz) to separate them from the rather broad-band pulsed radiation. Small differential absorptions from, e.g., pressure-broadened molecular transitions, can be detected. Other extremely sensitive laser absorption spectroscopy techniques have been described in [9.185,186]. 

An in-situ X-ray fluorescence microscopy combined with an X-ray absorption spectroscopy technique has been reported in order to investigate the Li2S batteries during their electrochemical cycling (71). The evolution of morphology changes of the electrode is monitored... 

A. Wolska, K. Lawniczak-Jablonska, M. Klepka, M.S. Walczak, A. Misiuk, Local structure around Mn atoms in Si crystals implanted with Mn-tstudied using x-ray absorption spectroscopy techniques. Phys. Rev. B 75(11), 113201 (2007)... 

Abstract In this chapter the reader can find an overview on the UV-vis absorption spectroscopy technique. A very brief introduction on the nature and formation of the electronically excited states is functional to the following discussion on the characteristics, and interpretation of UV-vis absorption spectra. The typical instrumentation is also schematically described, and a particular emphasis is devoted to the possible qualitative and quantitative information that can be obtained with this kind of measurements. Practical indications to obtain accurate and reliable experimental results were introduced with the aim to help the readers that will approach for the first time this fundamental experimental technique. The chapter ends with the discussion of a few examples, taken from the literature, with the aim to make clear the investigative great potentialities of this spectroscopy in different fields. 

The rate coefficient of the reaction of NO3 with Af,Af-dimethylacetamide has been measured by El Dib and Chakir (2007) using the laser photoly sis-UV-visible absorption spectroscopy technique. The measurements are given in table VIII-B-7 and are shown in figure VIII-B-2. An unweighted fit to the data leads to the Arrhenius expression ... 

Myerson s investigation employed the ARAS (atomic resonance absorption spectroscopy) technique to monitor the formation of O atoms behind incident shock waves. Mixtures studied were 0.1, 1.0, and 10% NO in Ar temperatures varied from 2600 to 6300 K, although only a portion of this range was suitable for determining the dissociation rate. A five-reaction model was employed to match computed and measured rates of O-atom formation. 

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